An experimental study of leakage current is presented in a semi-insulating（SI） Ga As photoconductive semiconductor switch（PCSS） with voltages up to 5.8 kV（average field is 19.3 kV/cm）. The leakage current increa...An experimental study of leakage current is presented in a semi-insulating（SI） Ga As photoconductive semiconductor switch（PCSS） with voltages up to 5.8 kV（average field is 19.3 kV/cm）. The leakage current increases nonlinearly with the bias voltage increasing from 1.2×10^-9 A to 3.6×10^-5A. Furthermore, the dark resistance, which is characterized as a function of electric field, does not monotonically decrease with the field but displays several distinct regimes. By eliminating the field-dependent drift velocity, the free-electron density n is extracted from the current, and then the critical field for each region of n（E） characteristic of PCSS is obtained. It must be the electric field that provides the free electron with sufficient energy to activate the carrier in the trapped state via multiple physical mechanisms, such as impurity ionization, fielddependent EL2 capture, and impact ionization of donor centers EL10 and EL2. The critical fields calculated from the activation energy of these physical processes accord well with the experimental results. Moreover, agreement between the fitting curve and experimental data of J（E）, further confirms that the dark-state characteristics are related to these field-dependent processes. The effects of voltage on SI-Ga As PCSS may give us an insight into its physical mechanism.展开更多
This essay argues that black and white cinema spawned a resistance to changing times that is still very present in the new generation of directors who follow classic film traditions while subverting them with consiste...This essay argues that black and white cinema spawned a resistance to changing times that is still very present in the new generation of directors who follow classic film traditions while subverting them with consistent narrative inventions.The Artist,the best picture Oscar award winner in 2012,is an example of this resistance as it pays homage to some of the greatest silent films of the first two or three decades of cinema history.“The Dark Side of the Screen”aims to underline that there is an unchanging power of the phantasmagoria so present in black and white movies,produced not only in the silent era but also in film noir through lighting effects and camera angles which characterize the work of major noir directors like Fritz Lang,Billy Wilder,and Orson Welles,who knew everything about the unutterable mysteries hidden on the dark side of the screen.展开更多
In our trials, from 2007 to 2008, of mass production of seedlings of Hizikiafusiformis using synchronization techniques, problems of a ＂dark thalli＂ phenomenon and epiphytes contamination severely threatened the hea...In our trials, from 2007 to 2008, of mass production of seedlings of Hizikiafusiformis using synchronization techniques, problems of a ＂dark thalli＂ phenomenon and epiphytes contamination severely threatened the health of juvenile seedlings. In this investigation, we optimized conditions for improving the growth of juvenile seedlings. Seven string collectors were seeded with zygotes and a series of experiments were conducted including direct exposure to solar irradiance, co-culture with Ulva spp. and treatment with sodium hypochlorite. It was found that direct exposure to solar irradiance （maximum： 1 740 μmol photons/（m2.s）） for 2 h per day could efficiently enhance the growth of young seedlings and simultaneously inhibit the growth of epiphytic algae. In this treatment, 50-day old seedlings could reach an average of 0.44 cm in length and possess up to nine leaflets. However, a single treatment with 18-mmol/L sodium hypochlorite for 10 rain severely harmed 15-day old seedlings. In comparison, weekly treatment with 2.2-mmol/L sodium hypochlorite for 10 rain brought no apparent harm to seedlings and eliminated epiphytic algae efficiently. However, this treatment significantly increased the detachment rate of seedlings, Inoculating Ulva spp. onto the collector caused a dramatic decrease in the number of seedlings. However, the growth of the remaining seedlings appeared unhampered. All collectors except the control were daily sprayed with a high pressure water jet from the 84 day post fertilization. From the first day to 50th day, no ＂dark thallus＂ was observed on any of the seven collectors. We believe that well-timed daily exposure to solar irradiance would favor H. fusiformis in its early growing stages.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.31470822)the Advanced Research Foundation of China(Grant Nos.9140A05030114DZ02068,9140A07030514DZ02101,and 9140A07010715DZ02001)
文摘An experimental study of leakage current is presented in a semi-insulating（SI） Ga As photoconductive semiconductor switch（PCSS） with voltages up to 5.8 kV（average field is 19.3 kV/cm）. The leakage current increases nonlinearly with the bias voltage increasing from 1.2×10^-9 A to 3.6×10^-5A. Furthermore, the dark resistance, which is characterized as a function of electric field, does not monotonically decrease with the field but displays several distinct regimes. By eliminating the field-dependent drift velocity, the free-electron density n is extracted from the current, and then the critical field for each region of n（E） characteristic of PCSS is obtained. It must be the electric field that provides the free electron with sufficient energy to activate the carrier in the trapped state via multiple physical mechanisms, such as impurity ionization, fielddependent EL2 capture, and impact ionization of donor centers EL10 and EL2. The critical fields calculated from the activation energy of these physical processes accord well with the experimental results. Moreover, agreement between the fitting curve and experimental data of J（E）, further confirms that the dark-state characteristics are related to these field-dependent processes. The effects of voltage on SI-Ga As PCSS may give us an insight into its physical mechanism.
文摘This essay argues that black and white cinema spawned a resistance to changing times that is still very present in the new generation of directors who follow classic film traditions while subverting them with consistent narrative inventions.The Artist,the best picture Oscar award winner in 2012,is an example of this resistance as it pays homage to some of the greatest silent films of the first two or three decades of cinema history.“The Dark Side of the Screen”aims to underline that there is an unchanging power of the phantasmagoria so present in black and white movies,produced not only in the silent era but also in film noir through lighting effects and camera angles which characterize the work of major noir directors like Fritz Lang,Billy Wilder,and Orson Welles,who knew everything about the unutterable mysteries hidden on the dark side of the screen.
基金Supported by the National High Technology Research and Development Program of China (863 Program) (Nos. 2006AA10A412 2006AA10A416)+1 种基金Main Program of National Science Infrastructure Platform, a project from the Ministry of Science and Technology of China (No. 2006DKA30470-017)a non-profit program from the Ministry of Agriculture of China (No. 200903030)
文摘In our trials, from 2007 to 2008, of mass production of seedlings of Hizikiafusiformis using synchronization techniques, problems of a ＂dark thalli＂ phenomenon and epiphytes contamination severely threatened the health of juvenile seedlings. In this investigation, we optimized conditions for improving the growth of juvenile seedlings. Seven string collectors were seeded with zygotes and a series of experiments were conducted including direct exposure to solar irradiance, co-culture with Ulva spp. and treatment with sodium hypochlorite. It was found that direct exposure to solar irradiance （maximum： 1 740 μmol photons/（m2.s）） for 2 h per day could efficiently enhance the growth of young seedlings and simultaneously inhibit the growth of epiphytic algae. In this treatment, 50-day old seedlings could reach an average of 0.44 cm in length and possess up to nine leaflets. However, a single treatment with 18-mmol/L sodium hypochlorite for 10 rain severely harmed 15-day old seedlings. In comparison, weekly treatment with 2.2-mmol/L sodium hypochlorite for 10 rain brought no apparent harm to seedlings and eliminated epiphytic algae efficiently. However, this treatment significantly increased the detachment rate of seedlings, Inoculating Ulva spp. onto the collector caused a dramatic decrease in the number of seedlings. However, the growth of the remaining seedlings appeared unhampered. All collectors except the control were daily sprayed with a high pressure water jet from the 84 day post fertilization. From the first day to 50th day, no ＂dark thallus＂ was observed on any of the seven collectors. We believe that well-timed daily exposure to solar irradiance would favor H. fusiformis in its early growing stages.
